faking top level anonymous unions

gistfile1.c

#include <stdint.h>
#include <stdio.h>

uint32_t u32 = 0;
extern uint8_t u8[4] __attribute__((alias("u32")));

int main() {
    printf("%08x\n", u32);
    u8[0] = 1;
    printf("%08x\n", u32);

    return 0;
}

Doesn't work with -O2 :x Aliasing rules...